Protection of cattle against heartwater in Botswana: comparative efficacy of different methods against natural and blood-derived challenges
Simpson, B.C.; Lindsay, M.S.; Morris, J.R.; Muirhead, F.S.; Pollock, A.; Prichard, S.G.; Stanley, H.G.; Thirlwell, G.R.; Hunter, A.G.; Bradley, J.
Veterinary Record 120(6): 135-138
1987
ISSN/ISBN: 0042-4900 PMID: 3604029 Document Number: 303759
Five groups of Tswana-cross castrated male cattle between 20 and 30 months of age (a total of 158 animals) were transported from a ranch in a heartwater-free area of south Botswana to a feedlot near Gaborone in the east of Botswana where heartwater is endemic. On arrival, one group was vaccinated i/v with the Onderstepoort sheep blood heartwater vaccine, one group was vaccinated i/v with the new Onderstepoort tick-derived heartwater vaccine and a third group was vaccinated s/c with this tick-derived vaccine. Vaccine reactions were blocked with long acting oxytetracycline on the first day of fever. A fourth group had a series of injections of long acting oxytetracycline on days 0, 7, 14 and 21 after arrival, and a fifth served as untreated controls. The animals remained at the feedlot for 65 days during which time they faced a low level of challenge by Amblyomma hebraeum ticks. None contracted heartwater and so they were then challenged, together with a further group of control cattle, with a dose of the sheep blood vaccine. Some animals in all groups had severe heartwater reactions and died despite therapy, but 76.7%, 64.5% and 74.3% of the cattle in the blood vaccine, i/v tick vaccine and long acting oxytetracycline groups, respectively, were resistant to challenge, compared with 48.3% of the s/c tick vaccine group and 36.4% of the controls. It was concluded that i/v vaccination of susceptible adult cattle with either the blood or the tick-derived vaccine needs careful monitoring in the month after vaccination and does not necessarily result in immune animals. No significant difference was demonstrated between the two vaccines in the degree of protection conferred. The results with long acting oxytetracycline suggested either that low levels of oxytetracycline persisted for extended periods of time or that the drug in this formulation induced a non-specific immunostimulant effect.